1. Field
Exemplary embodiments of the present disclosure relate to a fixing device and an image forming apparatus including the fixing device, and more specifically, to a fixing device that applies heat and pressure to a recording medium at a nip formed between a fixing member and a pressing member to fix an image on the recording medium, and an image forming apparatus including the fixing device.
2. Description of the Background Art
Related-art image forming apparatuses, such as copiers, facsimile machines, printers, or multifunction apparatuses having at least one of copying, printing, scanning, and facsimile functions, typically form an image on a recording medium according to image data. Thus, for example, a charger uniformly charges a surface of an image carrier; an optical writer emits a light beam onto the charged surface of the image carrier to form an electrostatic latent image on the image carrier according to the image data; a development device supplies toner to the electrostatic latent image formed on the image carrier to make the electrostatic latent image visible as a toner image; the toner image is directly transferred from the image carrier onto a recording medium or is indirectly transferred from the image carrier onto a recording medium via an intermediate transfer member; a cleaner then cleans the surface of the image carrier after the toner image is transferred from the image carrier onto the recording medium; finally, a fixing device applies heat and pressure to the recording medium bearing the toner image to fix the toner image on the recording medium, thus forming the image on the recording medium.
Such a fixing device may include a cylindrical metal member to heat the fixing device effectively to shorten a warm-up time or a time to first print (hereinafter also “first print time”). Specifically, the metal member is provided inside a loop into which an endless fixing belt is formed, facing a portion or the entire of the inner circumferential surface of the fixing belt. The metal member is heated by a built-in or external heater so as to heat the fixing belt. A pressing roller presses against the outer circumferential surface of the fixing belt at a position corresponding to the location of the metal member inside the loop formed by the fixing belt to form a nip between the fixing belt and the pressing roller through which the recording medium bearing the toner image passes. As the recording medium bearing the toner image passes through the nip, the fixing belt and the pressing roller apply heat and pressure to the recording medium to fix the toner image on the recording medium.
Such a fixing device is described, for example, in JP-2008-158482-A. The fixing device disclosed therein has the advantage of preventing faulty fixing even when the warm-up time and/or first print time are shortened to speed up the fixing process. Although generally successful for its intended purpose, however, better fixing performance of fixing images are needed to meet users' demand for higher image quality. To cope with such challenges, for example, it is conceivable to increase the width and/or surface pressure of the nip. For such a configuration, however, although the fixing performance of a fixing image is enhanced, cockling might occur in a recording medium discharged from the nip. Alternatively, friction resistance at the nip might be increased, resulting in increased driving torque.